Field of the Invention
The present invention relates to an optical apparatus including a reflective light modulator and an image projection apparatus using the optical apparatus.
Description of the Related Art
Image projection apparatuses (projectors) display an image by introducing a light flux emitted from a light source through an integrator optical system (illumination optical system) to a light modulator and projecting the light modulated by the light modulator depending on an input image signal through a projection optical system. Such image projection apparatuses include ones using a reflective light modulator as the light modulator, such as a reflective liquid crystal panel or a mirror light modulator.
Japanese Patent Laid-Open Nos. 10-274810 and 2002-268007 each disclose a projector that separates a white color light from the light source into three color lights, namely, an R light, a G light and a B light, introduces the three color lights to three reflective liquid crystal panels, combines the color lights from the three reflective liquid crystal panels with one another by a cross dichroic prism and then projects the combined light.
On the other hand, Japanese Patent Laid-Open No. 11-316356 discloses a projector having a similar configuration to those of the projectors disclosed in Japanese Patent Laid-Open Nos. 10-274810 and 2002-268007 while including a Philips-type dichroic prism instead of the cross dichroic prisms.
Each of the projectors disclosed in Japanese Patent Laid-Open Nos. 10-274810 and 2002-268007 causes an S-polarized light or a P-polarized light separated by a polarization beam splitter from the light from the light source to enter the cross dichroic prism to separate the polarized light into the three color lights and then combines, by the cross dichroic prism, the three color lights as P-polarized lights or S-polarized lights reflected by the reflective liquid crystal panels. As described above, the lights entering the cross dichroic prism from the polarization beam splitter and the reflective liquid crystal panels are the S- and P-polarized lights. For this reason, multiple dichroic films provided to the cross dichroic prism each need to have a sufficient dichroic characteristic for both the P-polarized light and the S-polarized light.
However, such a dichroic film typically has a characteristic that a cutoff wavelength thereof largely shifts depending on a ray incident angle. In addition, since the ray incident angle of the light from the polarization beam splitter to the dichroic film and the ray incident angle of the light from the reflective liquid crystal panel to the dichroic film are opposite to each other, a shift direction of the cutoff wavelength is inversed. Thus, a light amount loss of a spectrum component of the light from the light source around the cutoff wavelength of the dichroic film becomes large, which results in a decrease of brightness of a displayed image (projected image) and in an increase of color unevenness of the projected image.
In contrast, in the Philips-type dichroic prism used in the projector disclosed in Japanese Patent Laid-Open No. 11-316356, the ray incident angle to the dichroic film is close to 0 degree, differently from the cross dichroic prism.
This results also in a decrease in a dependence on an incident angle to the dichroic film, which enables reducing the light amount loss around the cutoff wavelength further than in the projectors disclosed in Japanese Patent Laid-Open Nos. 10-274810 and 2002-268007. However, decreasing an F-number of its illumination optical system in order to further increase an amount of the light entering the reflective liquid crystal panel increases the ray incident angle to the dichroic film. This increase in the ray incident angle consequently increases the light amount loss around the cutoff wavelength, which decreases the brightness of the projected image.
On the other hand, in the projector disclosed in Japanese Patent Laid-Open No. 2002-268007, the reflective liquid crystal panels are arranged such that their short sides (short-side directions) extend parallel to a section including an optical axis of its illumination optical system and including a normal to the dichroic film of the cross dichroic prism. This arrangement aims to reduce the color unevenness by decreasing the ray incident angle to the dichroic film. However, since this projector has a configuration in which light rays enter the reflective liquid crystal panel non-telecentrically, each light ray reaches the dichroic film at an incident angle larger than a maximum incident angle defined by an F-number of the illumination optical system. This results in an undesired increase in the light amount loss around the cutoff wavelength.
Japanese Patent Laid-Open No. 2002-268007 discloses a configuration that, for the above-described purpose, reduces number of lens cells of each of first and second fly-eye lenses included in the illumination optical system in a film surface direction of the dichroic film and that compresses a width of a light flux by using a compression optical system such as a cylindrical lens in that direction (compression direction). However, since the compression of the light flux undesirably decreases a degree of parallelism of the light flux, sizes of light source images formed near the lens cells of the second fly-eye lens increase in the compression direction, which increases an amount of a light component protruding outside (not entering) apertures of the lens cells. Consequently, the projector disclosed in Japanese Patent Laid-Open No. 2002-268007 in which the short-side direction of each reflective liquid crystal panel and a direction in which the size of the light source images increases coincide with each other has an increased light amount loss, which further decreases the brightness of the projected image.
As described above, the conventional projectors using the dichroic prism that separates the light toward the multiple reflective light modulators and combines the separated lights therefrom can achieve a sufficient color unevenness reduction, but cannot prevent or insufficiently reduces the decrease in the brightness of the projected image.